CG Board Class 8 Science Chapter 17 Solutions: Adolescence (किशोरावस्था) – 2026-27

• English: Mention the main characteristics of adolescence?
• Answer:
• English: The main characteristics of adolescence include:

1. Increase in Height: Sudden growth in height due to elongation of long bones of arms and legs.
2. Change in Body Shape: Broadening of shoulders and wider chest in boys; widening of hips below the waist in girls.
3. Voice Change: Growth of the voice box (larynx), leading to a prominent Adam’s apple in boys and a cracking or hoarse voice.
4. Increased Secretion of Skin Glands: Secretion of sweat and sebaceous (oil) glands increases, often causing acne and pimples on the face.
5. Development of Sex Organs: Testes and ovaries mature completely and begin to produce gametes (sperms and ova).
6. Appearance of Secondary Sexual Characters: Growth of facial hair (moustache and beard) in boys and breast development in girls.

• English: What are the reasons of acne and pimples on the face of adolescents?
• Answer:
• English: During puberty, the activity and secretion of sweat glands and sebaceous (oil) glands in the skin increases significantly. The excessive secretion of oil traps dirt and bacteria in skin pores, causing inflammation that leads to acne and pimples on the face.

• English: Why do adolescents feel insecure?
• Answer:
• English: Adolescents often feel insecure while trying to adjust to the rapid physical, mental, and hormonal changes taking place in their body and mind. However, adolescents should know that these bodily changes are a completely natural part of growing up and there is no reason to feel insecure.

• English: What are the main differences between viviparous and oviparous animals?
• Answer:
• English:
• Comparison Table:
• Hindi:

• English: What is fertilisation? Explain.
• Answer:
• English:
• Definition: The fusion of a male gamete (sperm) with a female gamete (egg or ovum) to form a zygote is called fertilisation.
• Types of Fertilisation:

1. Internal Fertilisation: Fertilisation that occurs inside the female body (e.g., human, cow, cat).
2. External Fertilisation: Fertilisation where fusion of egg and sperm takes place outside the female body in water (e.g., frog, fish).

• Hindi:

• English: Name the hormones responsible for the changes occurring in adolescence at puberty.
• Answer:
• English:

1. Male Hormone: Testosterone (released by the testes), responsible for male secondary sexual characteristics like facial hair growth.
2. Female Hormone: Estrogen (produced by the ovaries), responsible for female secondary sexual characteristics like breast development.
3. Control Hormone: Hormones secreted by the Pituitary gland, which regulate the release of testosterone and estrogen.

• Hindi:

• English: What is the span of reproductive life in females?
• Answer:
• English: In human females, the reproductive phase of life begins at puberty (around 10 to 12 years of age) with the onset of menstruation (menarche) and generally lasts until the age of approximately 45 to 50 years when menstruation stops (menopause).

• English: What do you understand by secondary sexual characters?
• Answer:
• English: Physical features that develop during puberty under the influence of sex hormones and help to distinguish males from females visually are called secondary sexual characters.
• In Boys: Growth of facial hair (moustaches and beard), deepening of voice, hair on chest and pubic region.
• In Girls: Development of breasts, growth of hair in armpits and pubic region, widening of hips.

• English: Which chromosomes are responsible for the determination of sex in human?
• Answer:
• English: Human cell nuclei contain 23 pairs of chromosomes, out of which 1 pair consists of sex chromosomes named X and Y. Females have two X chromosomes (XX), while males have one X and one Y chromosome (XY). The sex of the unborn baby is determined by the father’s sperm: an X-bearing sperm produces a female child (XX), whereas a Y-bearing sperm produces a male child (XY).

• English: Why the diet of an adolescent should be carefully planned?
• Answer:
• English: Adolescence is a period of rapid physical growth and development. Therefore, an adolescent’s diet must be carefully planned to be a balanced diet containing proteins, carbohydrates, fats, vitamins, and minerals (such as iron and calcium) in requisite proportions to nourish growing bones, muscles, and organs properly.

• English: Why it is important to maintain personal hygiene during adolescence?
• Answer:
• English: During adolescence, the increased activity of sweat and oil glands makes the body sweaty and smelly. If daily cleanliness and proper washing are not maintained, it can cause bacterial and fungal infections. Furthermore, girls must maintain hygiene during menstruation to prevent reproductive tract infections.

• English:
• Mechanism & Chromosomal Structure: Every human cell nucleus contains 23 pairs of chromosomes, including 1 pair of sex chromosomes. Females have XX sex chromosomes and produce ova with only X chromosomes. Males have XY sex chromosomes and produce two types of sperms: 50% carrying an X chromosome and 50% carrying a Y chromosome.
• Fertilisation Outcomes:

1. If an X-bearing sperm fertilises the ovum, the resulting zygote is XX, which develops into a female child.
2. If a Y-bearing sperm fertilises the ovum, the resulting zygote is XY, which develops into a male child.

• Diagrammatic Flow Explanation:

Mother (XX) × Father (XY)

Egg (X) + Sperm (X) → Zygote (XX) ⇒ Female Child

Egg (X) + Sperm (Y) → Zygote (XY) ⇒ Male Child

• Hindi:

• English:
• Oviparous Animals: Animals that lay eggs covered with a shell, inside which embryonic development occurs outside the mother’s body (e.g., hen, lizard, frog, birds).
• Viviparous Animals: Animals that give birth directly to fully formed young ones after internal development inside the uterus (e.g., human, cow, dog, cat).
• Hindi:

• Data Table:
• Conclusions drawn from the Graph:
• English:

1. At birth (0 years), the average height of both boys and girls is identical (51 cm).
2. From age 4 to 8 years, boys grow slightly faster in height than girls.
3. Around age 12 years (onset of puberty), girls grow faster than boys and temporarily surpass boys in height (131 cm vs 127 cm).
4. By 16 years, both reach the same height, and by 20 years, boys attain a higher maximum height than girls (171 cm vs 163 cm).

• Hindi: